Color television registration control system



J. S. BRYAN Aug. 21, 1956 COLOR TELEVISION REGISTRATION CONTROL SYSTEM Filed June 50, 1951 COLOR TELEVISION REGISTRATION CONTROB SYSTEM Philadelphia, Pa., aissignor toV Philco James S, Bryan,

Philadelphia, Pa., a corporation OfPenn- Corporation, Sylvania u `The present invention relates to electrical systemsand more particularlyV to cathode-ray tubel systems* compris ing a beam intercepting member and an indexing member which is arranged in cooperative relationship with the beam intercepting member and is adapted 'to'. produce a signal Whosetirne of occurrence is indicative oftheposition of the'cathode-ray beam relative tothe beainr inl tercepting member.

' The invention is particularly adapted for use and will be `described in connection with a color televisionv image presentation system utilizing-a single rcathode-ray tube having'a beam intercepting, image forming screen'mein'- b er'comprising vertical stripes of luminescentraterialsl These "stripes are preferably arranged in laterallyl'displ'a'ced color triplets', each triplet comprising three vertical phos'l phor stripes which respond to electronv impingemeuthto produce light of the dilerent primary colorsl Theo'rder of arrangement of the stripes may be such that the nor? rn'ally horizontally-scanning cathode-ray bea'rrfprodces red, greenand blue light successively. From acolo television'recei'ver there may then be supplied three sepa-` rate video signals, each' indicative of aditferentfpimar'y color component of a televised'scene, which` sig 1als"are sampled sequentially and utilizedto control`the'intensity 4of the cathode-ray beam. For proper vcolor *rendi` tion, itis then4 required that, as the phosphor stripes pro'- ducingleach of the primary colors of lightjare impin'gd bythe'cathode-ray beam, the intensity yof thev bembe simultaneously controlled in response to the contempo-l raneous `Value of the video signal representing the 'correi sponding color 'component of the televised image.' Howl ever', since the rate at which the beam scans across the phosphor'stripes of the'scr'een may vary, due, for exi ample, to non-linearity of the'beam yd'eiiecting signal, or due to a non-uniform distribution of the colo'rtriplets on the screen surface, the times at which the samples ofthe several video color signals should'betaken will generally not occur exactly periodicallyl To obtain proper tim'f ing of the sampling operations, it is therefore desirable to derive signals indicative of the instantaneous position of the cathode-ray beam upon the image-forming screen', and to utilize these vindexing signals to control the'times at which samplings of the several colorsignals are'eiiectedl The said indexing signals may be derived from apluifality of -stripe members arranged on the beam.y intercepting screen structure, each adjacent a triplet, so that, when the beam scans the screen, the indexing vstripes 'are excited inspaced Vtime sequencerelative' to the scanning ofthe color triplets and a seriesA of pulses is" vgenerated in a'isuita= ble output electrode system of 4the cathode-'raytube'.v4

The indexing stripes may compriseaimaterialfhavf ing secondary-emissive properties which diier the secondary-emissive' 'properties' ofthe remaihingportions of the Vbeam intercepting structure. For'exampllethe indexing stripes may consist of a high atomicnuinber material such as gold, platinum or tungsten'ior may consi's't' ot` certain oxides such as magnesium'oxide, andl the remainder' of lthe beam intercepting structure :may beprovided With a coatin'giof a material havingafdeteetably diie'r'nt" secondary-emissive ratio, suchl aluminum,

Uaitsd Sm Prem' 0 ICC Whichcoatingalso serves as a light reflecting mirror for the phosphorstripes in accordance with Well known practice. With such an arrangement the indexingv signals may bederived from a collector electrode arranged inY thefvicinity ofthe'screen structure. Alternatively, the indexing stripes may consist of a iiuorescentmaterial, such as `zincoxide, havinga spectral output intheV nonvisibie light region and the indexing signals may' bederived from a suitable photo-electric Vcell arrar'iged, for example, in'a sidewall portion of the cathode-,ray'tube out of the pathy of the cathode-ray beam and facingthe beam intercepting surfaceL of thescreen structure.

ln practice there exists the danger that thelnorrnally detectable Voltage indicatingthe impingeinent of lthe beam ontothe indexingstripes may be masked-or at least contaminated by'spur'ious voltages. Moreparticularly, it'isI found that, at the high acceleratin'gvoltages of :the order of 1Q to 20 kilovolts used in thecathode-ray tubes for thesys'tems undercons'ideration, only aurela'tively small diierence in the secondary-emissive `ratio of the materials" ,ofv the indexing stripes and-of the remainder oft'h'e'screen'structure can be realized and that, in the heretofore proposed systems, the presence of video signals and noise voltages in the collector electrode' ysystem may' significantly diminish the etective valuev of the ix'iclexing` signal. Similarly, in those instances in which the indexing-signal isprodu'ced by means of a`photoelectric detector andindexing stripes comprisingla iluorescent material which produces'light'inthe non-visible regionA of' the spectrum, the detector mayhallso bevactuated by soft 'Xlrays `which are produced by the high `v oltf ag'e beam" or by extraneous light from sourcesexternal to the cathode-ray tube or from the phosphor stripes of the 'color triplets, the latter light in some instances penetrating the aluminum mirror coating superimposed on the color' stripes. I

yIn the copending application of' E. M. Creamer, ylr., et'aL, Serial No. 240,324`iiled'August 4, 1951, In'ow Patent'No. 2,6"67,534'"granted January 26', 1954, there'have beenide'scribed systems by meansof'whichthe desired indexingv information may be obtained in areadilyV usable foriri with a minimum ofil components atthe video signal frequencies' appearing in the indexing signalkcircuit'sl More particularly, and inv accordance' with the principles set forth in the said copending application, uselis made of'theviinding that the scanning of the index*- ing stripes by the electron beam will produce, inthe 'col-l lector circuit of the cathode-ray tube, signal components which represent modulation products as determined j by theintensi'ty'variations*of the ,beam and the ratefof scanning of ,the indexstripes. Accordingly, by addition# allyV varyingV the' intensity of the beam atta pilotfcarrier frequency rate Widely dierent fromytherate' at`which the beam intensity is varied by the` video signal, an output'signal is produced inthe collector electrode of the cathode-ray tubecomprising, as one comp'onent,Ino dulation'p'roductsproportional to the' pilot carrier frequency and the rate of scanning the index stripes. yBef cause of their Widely different frequency range, these modulationproducts may readilyvbe separated from those generatedjmodulation products which are proportional tothe video signal frequencies vand the ratev of scanning offthe index stripes. The pilot carrier modulation products consist essentially of a carrier Wave atthepilot carrier frequency and sidebands representing the Asum and diierence lof the pilot carrier frequencyV and the ratevoi scanning the indexvstripes. Any changev in the rate of scanning of the index stripesv will be indicated bya change infthe frequencies of the sidebands and accordingly the separated signalv or'one of-its `sidebands may be used as anindexingr signal'of lhigh quality.

in some instances, secondary factors within ode-ray tube system above described may operate to contaminate the indexing signal so produced so that the signal is no longer precisely definitive of the absolute position of the cathode-ray beam. More particularly, it has been found that, due to manufacturing tolerances of the beam generating elements of the cathode-ray tube, the beamcurrent versus control-voltage characteristc of the cathoderay tube may exhibit serious departures from linearity so that undesirable cross-modulation effects may be produced when the video signal and the pilot carrier signal are applied to the intensity control element thereof. The cross-modulation products so produced introduce new components which similarly vary lthe intensity of the beam and appear as spurious signals in the output indexing circuit of the cathode-ray tube. Since the heterodyne components of the cross-modulation products may have frequencies within the frequency band of the indexing signal, their presence may undesirably affect the system operation and bring about inaccurate or at least degraded reproduction of the colors of the image.

It is an object of the invention to provide an improved cathode-ray tube system of the type in which the position of the electron beam relative to a beam intercepting member is indicated by a signal produced by an indexing member arranged in cooperative relationship to the beam intercepting member.

Another object of the invention is to provide a cathoderay tube system of the type in which the position of the electron beam is indicated by a signal produced by an assoeiated indexing member and in which a clearly defined indexing signal is generated.

A specic object of the invention is to provide a cathoderay tube system operating on principles above outlined, and in which spurious signals normally brought about by a cross-modulation action of video and carrier signals applied to the beam intensity control electrode of a cathode-ray tube are avoided.

These and further objects of the invention will appear as the specification progresses.

In accordance with the invention, the foregoing objects are achieved by employing a cathode-ray tube having disposed therein a beam intercepting structure comprising beam position indicating elements arranged in predetermined geometric relationship to other portions of the beam intercepting structure. These beam indicating elements, as above pointed out, may be in the form of spaced stripes and are characterized by values of secondaryemissive ratio or by spectral emission characteristics which diier from those characterizing other regions of the beam intercepting structure when electrons of the cathode-ray beam impinge thereon. When the intensity of the beam is simultaneously varied at a pilot carrier rate and at a rate determined by a color video signal having color information occurring at the repetition rate at which successive color triplets of the beam intercepting structure are scanned, the action of the beam, as it scans the indexing stripes, will in turn produce secondary electrons which generate, in the output circuit of the tube, two component signals. One of the component signals has a frequency proportional to the product of the video signal intensity variations of the beam and the rate of scanning of the indexing stripes, and the other of the component signals has a frequency proportional to the pilot carrier intensity variations of the beam and the rate of scanning of the indexing stripes. Since the latter component signal may be made to have a frequency spectrum widely separated from the frequency spectrum of the rst component signal by an appropriate selection of the pilot carrier frequency, the two components may be readily separated in the output collector system of the cathode-ray tube. Furthermore, since the sidebands of the said latter component signal are determined by the algebraic sum of the pilot carrier frequency and the rate of scanning of the index stripes, any departures of the scanning velocity of the the cathfi beam from linearity or non-uniformities in the position and distribution of the index stripes will be reccted as changes in the frequency of the sidebands, and accordingly the latter component or a sideband thereof may be utilized as an indexing signal.

When the simultaneous variations of the intensity of the beam are effected by applying a video signal and a pilot carrier wave to the control electrode of the cathode-ray tube, it is found that in some instances the non-linearity of the beam-current versus control-voltage characteristic of the tube may produce cross-modulation products of the applied signals and thereby produce undesired signals which additionally vary the intensity of the beam. These additional variations of the intensity of the beam produce spurious signals in the output indexing circuit of the tube because they represent sum and difference frequencies which are the same as the sum and difference frequencies produced by the heterodyne action of the pilot carrier and the index stripes.

In accordance with the invention, the simultaneous variation of the intensity of the cathode-ray beam at the desired pilot carrier frequency and at the impressed video color Wave frequency is effected, without simultaneously varying the intensity of the beam at frequencies producing undesired spurious signals in the output indexing circuit of the tube, by applying to the control system of the tube the video signal together with first and second index control signals. The latter signals are so related that their cross-niodulation products comprise one component having a frequency at the desired pilot carrier rate, and other components having frequencies so widely different from the pilot carrier rate that the latter components, and their heterodyne products with the indexing stripes, may be readily discriminated against in the index output circuit of the cathode-ray tube. More specically, and in accordance with the invention, there are applied to the intensity control system of the cathode-ray tube, the color video signal having a color repetition rate approximating the rate of scanning of the color triplets of the image producing screen, a first index control signal having a frequency which is relatively high with respect to the rate of scanning of the index stripes, and a second index control signal having a frequency equal to the algebraic sum of the frequency of the first index control signal and the desired pilot carrier frequency. Because of the non-linear characteristic of the beam intensity control system of the cathoderay tube, the electron beam is simultaneously varied in intensity not only at the video signal rate but also at rates proportional to the sum and difference frequencies of the above noted three signals applied to the control element. It will be noted that the algebraic sum of the first and second index control signals represents a signal at the desired pilot carrier rate so that the beam is accordingly varied in intensity at this rate. By a suitable selection of the frequency of the first index control signal, all of the remaining products of the cross-modulation action may be made -to have frequencies widely different from the desired pilot carrier and its heterodyne components with the indexing stripes, so that these other cross-modulation products and their heterodyne products with the indexing stripes may be readily cancelled or discriminated against in the output indexing circuit of the cathode-ray tube.

The invention will be described in greater detail with reference to the appended drawing forming part of the specification and in which;

Figure 1 is a block diagram, partly schematic, illustrating one embodiment of the invention,

Figure Z is a cross-sectional View, partly cut away, showing a portion of one form of beam interceptng structure for a cathode-ray tube which may be used in the system of the invention.

Referring to Figure l, the cathode-ray tube system shown therein comprises a cathode-ray tube it) containing, within an evacuated envelope 12, a conventionally constructed beam generating and accelerating gelectrode system f comprising ,a cathode '5114, a l, control ieleClOde 1-6 for=varying therintensityof thebeamV-a --focussingl electrode 18, wand L ai =,beam accelerating relec trode .whichsmay .consist of L a: conductive coatingy 4on .the yinner wallofthe envelopeanduwhichr.terminates-at a-point spacedrfrom the end face :22of-the tube in coniformance. with well-established practice. llSuita-ble 'Alleating means- (not shown) are provided;forfniaintainingfthe cathode t 14--at-its Ioperating temperature. :The electrode system so dened is energized from a suitable soureof Y potentialshown .as a; 4battery 24-having its negative pole connectedntmground l.and its-positivepole connected to the electr-ode il--andanbattery LZthhaving its negative pole connecteditothe positive -pole of -1 the battery 4=24 -andits\positive pole vconnected'to the accelerating elecf=trode 20. Inpracticethebattery v24 has a potential of vtherorder of l-to f3=kilovolts Whereas the battery 26 has apotential ofthe order of -l0 to 20 kilovolts. The .op- --erating potential Aof f the control electrode y16- may be 4`established' bya D.C.restorei-connected-vto the electrode 16 and consisting of adi-odel-Zappropriately peled and shunting a grid resistor 30. u'The cathodef14 may --be connected to a point of ground potentiall asshown.

A A deflection yoke 32, coupledto `horizontal and vertical Ideflect-ion circuits or" conventional -design,-is pro- -lvidedfor deflecting the generatedelectron beam across 'theface plateV 22 of the cathode-ray tube to forma raster rfthereon.

lThe end faceplate 22 of the tubegis `provided-with Va beaml interceptingstructurei314, onesuitable f ormA of AWhich-is -shown in 'detailfin"Figure 2. lIn "thearrange- `mentshown in Figure 2 the structure 34 is formed directly on. the faceplate L22. Howeverfthe structure'34 -may alternatively be formed on asu' able 'light transyparent'basevwhich is independentpf 'the facerjplate^22 land may `'be spaced f therefrom.` 'In the arrangement shown, theend'faceZZ, whichV in practice consists of glassghaving preferably substantially uniformjtransmisysion eharacteristicsfor the various',colors in theivisible spectrum, 'is provided with a plurality vof groups of elongated parallelly arranged stripes 316, 38 and4t),of, phos- 4' phor lmaterial which, Aupon `impingement by the cathoderay beam,"uoresce to produce lightlofthree ydilerent Qprimary colors. For example, the stripe 36 may consistofa :phosphor .which lproduces red light, the stripe B18-may consist of a phosphor Whichwrproduces :green light, and the striped() may consist of a phosphor which produces blue light. vEach of thergroups `of stripes may be termed a c,olor triplet and, as willbe vnotedgthe .,sequence ofthe stripesis repeated in consecutive, order over the area of the structure 34. Suitable materials onstituting V the ,phosphor stripes "3,6, 38 and 40, are yvelljrknown to thoseskilled inthe Lartas wellasjthe .method 0f applying the Same t0 the face Platani and 'further details lconcerning the. same y ares believed'to lbe unnecessary- Y g Inithe arrangement speciicallyushown, thejindexing signalis, produced bvmilizing .indexngstrpes of @given segondaryfemissiveratio differing Afrom the ,secondary- ,emissive ratio of Athe remainder ofthe beam intercepting structure, and fonti-risy purpose thestructure 34 further ,l comprises ay think electron permeable conductingI layer- 42 ,of lowsseeondary-emissiyity. A`The layer,42 is-arranged on the phosphor stripes 36, 38 ,andAtl,.andhpreferably furthenconstitutes ,ammirror -rellecting ylight generated at the ,phosphor stripes. in practice the layer 42 is,a light LArelieoting aluminum coating which `is formed `in well rknownfmanner. Qther metals capab1ef.offorming,a coatingl iin rthe manner, similar. to aluminum, and `having secondary-emissive ratios deteetably different from that f the. f, material, ,of ,the indexing `member, -.may alsoA ,be used 1vStien other `metalsgare, for example, magnesium tor-,beryllium ferraagedsonfthe. soaring-:41.2,1y over. `cozlsgctltive green stripes@t-:faresindexing; strips-i44=ggnsistgg .gf .a

l vias the indexingsignalpand accordingly terial having -.a1= secondany-emissi-xrzellratioA fdetectablyadif- :ferent {fromathat ofuthe materialsof eoatingg42g 'The stripes `.44 may consist ofigolrl or'othenwhighiatomio,nurn- *5 bermetals; such as platinum ornt-ungsten oraofanfoxide .such as 'magnesium oxide. "f

The beam: interceptingy structure so constituted: :ist connected to: thepositivef. pole of. the battery-26 byImeans of `a rsuita'olelead attached: toA the aluminum coating `42. i interposed; between the..endof :the acceleratingfanode "20 and-the..beam.intercepting 4strlucturefgZZ is a'naoutput collector electrodef46tconsistingof aringshaped-coating, "for,v1 examplev .ofsgraphite .or vofV silver,` ont the; wall off the t envelope. `Electrodel is .energized'througha load:fre sistorfi'from a suitablesourceiSt),l shownlasanbattery. The source 50 may-have apo-tentialof-` theorder.=off.3 kilovolts. Y f5 The cathode-ray beam in `itskhorizontal .-traveLacross "the beam intercepting structurevsimpinges successively on the coatingrliZ. and '-the:indexing.-stripesi44. When .the'beam is varied in'intensity at apilot carrier-rate in a manner later to.-be more ffully". pointed gout,;jthe scanningy `beam lwill `generate across the load-resistor 48 V2in-indexing signal made up of atcomponentatthefpilot carrier-rate and sidebands representing the sum xandfdify.ference frequencies of '.thepilot carr-ierufrequencvind the rate a-t whichy the index stripes are scanned by the cathode-ray beam. l Y' In atypical case, -the-pilot Vcarrier variationsA oilthe fintensity of the* beam mayoccur at a frequency yoti 5 gmc/sec.v and'when Ethel rate Aof scanning-the indexstripes :44 is approximately#million-per second',fas-1determined -fbythe'v horizontal "scanning rateand the numberpf'hin'dex stripes 44 '.impinged--per` scanning -per-iod, a modulated signal at 3&5.v nic/sec. andlvhaving' sidebandsat approximately 131.5 4and 45:5 mc/sec. -is produced. Changes in the rate of scanning of the indexstripesxlfi due-to v.nonflinearities of l:the ilbeamdeflection and/ or y.non-urliformities-of thefspacingsof theindex stripes,'-willproduce `corresponding. changes inthe frequencies of the sidebands. Therefore, 'the signal produced by -the intensity variations of the beamfat Ithe pilot` carrier frequencyor asideband-ofthis signalma'y be v.used-.as an-indexing`signal indicative. tof the position'oflthe beam -.onthe-surface -of therbeaminterceptingstructure 34. In the arrange- .ment specically` shown in Figure l the-*lower sideband; i. e., the sideband at approximately13ls5 -mc./sec., is utilized the 1`si`gnalgenerated across 'load resistor .648; is yapplied ythrough asidehand amplifier and amplitudelimiterzifZ to autilization'ci-rctit therefor consisting .of l, a miXeruiSl. .AmplierzSZ isigof conventional rdesign ,andjs' characterized I by a :band'pas's vresponse :which transmits and. amplies only.- signals havingI frequencies in the Yrangek of the-` above notedtlower sideband. The amplifier fmay= embody conventionali am- .,pltude limiting. vmeans byf whichany ,amplitudennodulation appearingron the signal-may;,berem'oved=andssthe amplifier; may;4 l,bef ,adaptedV ,to provide :the desi-redaampliyication fwithout phasel distortion ,ofthe, applied Csignal.

For thergproductign- Ofi, av @olor yirnageferr the `faceplate -ofvthe cathode-ray tube,there are-,provided celprrfsignal input terminals 60, 62. and/,64 xgvhichare suppliedgfromga ytelevisin receiver: with .-'Sgparate-vsgnals .-i.I,1.dl11 ;-.g.tL n, `red, green andvbluevcomp'onents -of t hle,.tele` v se jscene, respectively. The system@ then operates to efectively Convertthegef three wlor; signals imola-wave ,hagiagithe color information arranged in time referene` sequence so that'the-redh informatipn,Qcc-ursfwhen the-cath@ Iray -fbeamimpinges thergd-Stripef of. dwvbegm-,mersepting structure 34, thegreen ;information` occurs `uponl fpnggmentof;the-green-Stripgandathe blue tion occurs when the blue. stripeAO tislglirnppinged.

iThe conversion` 1of, the olor-signals into.- .with Ls,equgnfiallr v occurring; G0191 gerer@ brought about bya sampling procedure Connects @ash oftherinpgttar rier rate in accordance with common output channel, or may be effected by means of an equivalent modulation system suitably energized by the respective color signals and by appropriately phase related modulation signals. In the arrangement specifically shown, the desired conversion is effected by means of sine wave modulators 66, 68 and 'itl in conjunction with an adder 72. Modulators 66, 68 and 70 may be of conventional form and may each consist, for example, of a dual grid thermionic tube to one grid of which is applied the color signal from the respective terminals 60, 62 and 64, and to the other grid of which is applied a modulation signal. The modulation signals are derived from a pilot carrier oscillator 74 through a phase shifter 76, the latter being adapted to produce, by means of suitable phase shifting networks, three modulation voltages appropriately phase displaced. ln the arrangement specifically described, wherein the phosphor stripes 36, 38 and 4G (see Figure 2) are uniformly dis tributed throughout the width of each color triplet, the modulation voltages from the phase shifter, 76 bear a 120 phase relationship as shown.

The individual waves produced at the outputs of the modulators will be sine waves, each amplitude modulated by the color signal applied to the respective modulators and each having a phase relationship determined by the particular modulation signal applied. The three modulators are coupled with their outputs in common whereby the three waves are combined to produce a resultant wave having a frequency equal to that of the oscillator 74 and having amplitude and phase variations proportional to the amplitudes of the color signals. A band-pass filter 78, having a central frequency as determined by the frequency of the modulating signals applied to the modulators, may be arranged in the common output of the modulators to suppress undesirable modulation components.

As will be discussed presently, the pilot carrier oscillator 74 further cooperates with an index control oscillator 90 to vary the intensity of the cathode-ray beam at a pilot carthe principles set forth in the above referred to copending application of E. M. Creamer, et al. Accordingly, the oscillator 74 operates at a frequency outside the frequency spectrum of the video color wave applied to the control electrode 16 of the cathode-ray tube, i. e., at a frequency of 38.5 rnc/sec. as above specifically illustrated.

The resultant wave at the common output circuit of modulators 66, 68 and 70 is applied to the mixer 54, together with the indexing signal derived from the amplifier and limiter 52, to produce a heterodyne difference signal having amplitude and phase variations as determined by the amplitudes of the color signals at the terminals 60, 62 and 64 and having further phase (and/ or frequency) variations as determined by the variations in the rate of scanning the index stripes of the beam intercepting structure of the cathode-ray tube. It will be noted that, since the desired high frequency intensity variation of the cathode-ray beam and the modulation of the color signals at terminals 60, 62 and 64 are at the same frequency, the heterodyne difference signal produced by mixer 54 will have a central frequency equal to the average rate of scanning the index stripes, so that each successive color triplet of the structure 34 will be energized by successive cycles of the said difference signal.

Each of the color signals supplied to the input terminals of modulators 66, 63 and 70 will, in general, include a reference level component definitive of brightness. While each modulator may be constructed so as to transmit this reference level component to its output, in practice this is generally not done. Preferably, the three color signals are combined inproper proportions in an adder 72 to yield a single signal representative of the over-all brightness of the scene to be reproduced and this signal is in turn supplied to an adder 80 where it is combined with -the signal produced in the output of mixer 54.

The signal at the output of the adder thus comprises a reference level component establishing the brightness information of the image to be reproduced and a modulat-ed component establishing the chromaticity of the image. This signal is applied through an adder 32 to the control electrode 16 of the cathode-ray tube to thereby intensity modulate the cathode-ray beam in time sequence with the scanning of the electron beam over con secutive phosphor stripes of the beam intercepting structure.

ln order to simultaneously Vary the intensity of the cathode-ray beam at a rate producing, with the index stripes 44, the desired indexing signal, iirst and second index control signals are additionally applied to the control grid 16, These index control signals are so correlated that the heterodyne products thereof, brought about by the non-linearity of the control system of the cathoderay tube, contain a component which varies the intensity of the beam at the desired pilot carrier rate. For this purpose there is provided an index control oscillator which is coupled directly through connection 91 to the adder 32 and thereby supplies the first of the index control voltages to the control grid 16. The second index control voltage is produced by heterodyne action of the wave from oscillator 90 and a wave from the pilot carrier oscillator 74, for example by means of a mixer 92 which is coupled to the oscillator 96, and to the oscillator 74 through an isolation amplifier @4. @ne sideband of the heterodyne products so produced, i. e. the upper side band is applied through a band-pass lilter 96 to the adder 32 and thence to the control grid 16. Alternatively, the band-pass tilter 96 may be arranged to pass both the carrier component and the desired sideband product of the carrier from the oscillator 90 resulting from the modulation action by the mixer 92, thereby making unnecessary the direct link 91 between the oscillator 90 and the adder 82 above described. The described arrangement is preferred however, because it permits more precise control of the signals applied to the adder 32. A suitable frequency for the oscillator 90 is, for example, 100 mc./sec.

Briefly summarizing the above, it will be seen that there are three signals supplied to the control grid 16, as follows:

l. A video color signal having a frequency component corresponding to the rate of scanning the color triplets of the beam intercepting structure, i. e., a frequency component at approximately 7 mc./sec.

2. A lirst index control signal at a given frequency widely separated from the frequency of the video color signal i. e., at approximately lOO mc./ sec.; this signal being produced by the oscillator 90.

3. A second index control signal at a sum or difference frequency determined by the frequency of the first index control signal and by the desired pilot carrier rate of varying the intensity of the beam i. e., at approximately 138.5 mc./sec.; this signal being produced by the heterodyne action of the outputs of oscillators 74 and 90.

Because of the non-linear control-voltage versus beamcurrent characteristic of the tube 10, there will be produced sum and difference frequency components of the three applied signals so that the intensity of the beam will be varied simultaneously not only at rates determined by the three signals but also at rates determined by the interaction components.

From a consideration of the frequency values of the three signals applied to the control grid 16 and the frequency values of the interaction components, it will be seen that lone interaction component has the desired pilot carrier frequency. Therefore, the intensity of the beam will be varied in one instance at the desired pilot carrier rate, i. e., at 38.5 mc./sec. as determined by the beat frequency between the first index control signal at l0() mc./sec. and the second index control signal at 138.5 mc./sec. The subsequent heterodyne action between the so varied beam and the index stripes, i. e.,

agradece applied to vthecontrol grid16,nor their interaction prodf vucts, nor Ithe heterodyne products produced with vthe index ='stripes,with 4,the-exception -ofthe desired-index signal heterodyne product; have 'frequencyI values approximating the frequency of the desired indexing-signal. `Accordingly, thedesired indexsignaLma-y readily be separatedfffrom the remainingsignals--appearing-rin the output of 4tube'i0 `-by a suitable frequencyband-passsystem, for example by ymeans-of fthe y'sideband ampliiier-limiterf'l As -a-general rule, thenon-l-inear characteristic-'of the tube approximates a square law relationship sol'lthat vonly variations -of the intensityfof the beamfat-the apapl-iedffsignallfrequenciesf'atfrequencies -twice the signal lfrequencies, and'at'frequenciesf equal `to the sums and-differences of the signal frequencies need be considered. Under this condition the intensity variations of the beam occurring at'rthe -pilot frequencyare substantially constant notwithstandingizbeam intensity,variations` at other fre- .quencies produced, for example,bythe video color. signal. v`When ,the ,non-linear characteristic, ofthe tube does not .v-lpproximatera square law relationship, ,.-st'ant variations of the beam intensityat the ,piloticarrlier rate may nevertheless be obtained in accordanceswith 1.a further Ifeature yof the invention,I byjfurther applying to thecontrolsystem of the tube a compensating signalfat (the pilot frequency. '"Su'ch a compensating signal when applied to the cathode-ray tube in proper phase and amount, is heterodyned with the video color signal by the cathode-ray tube elements and thereby varies the intensity of the beam in a sense and by an amount cancelling the variations occurring at the pilot carrier rate. The compensating signal may be applied to the control electrode 16, by means of a phase and amplitude control 98 having its input connected to the isolation amplifier 94 and i-ts output connected to adder 82.

While I have described my invention by means of specic examples and in a specific embodiment, I do not Wish `to be limited thereto for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What I claim is:

l. A cathode-ray tube system comprising a cathoderay tube having a source of an electron beam, control means to vary the intensity of the beam, a beam intercepting structure for producing a rst given response upon impingement by said beam, said structure having portions thereof spaced apart and producing a second given response when said beam impinges thereon, and means to produce an output signal indicative of intensity variations of said beam and of said second given response, said control means being constructed and arranged so as to impart to said cathode ray tube a non-linear beam-current versus control-voltage characteristic producing nonlinear interaction of the intensity variations of said beam when a plurality of signals are applied to said control means, means for periodically deiiecting said beam across the beam intercepting structure to thereby successively scan said beam over said spaced portions, means for producing a first signal having a frequency spectrum of given maximum extent and being representative of desired variations of said first response, means for producing a second signal having a frequency greater than and widely different from the maximum frequency of said rst signal, means for producing a third signal having a frequency greater than the said maximum frequency of said first signal and differing from the frequency of said second signal by a predetermined value, means for applying said first, second and third signals to said control means, and means coupled to said output signal means for deriving therefrom an output wave having a component established by said second and third signals and substantially-com 10 '-zbythe Arate -of v-1scanaling-fof said @beam `loversaid spaced jportions.

l A cathode --ray tube-.system-.as claimedsn 1claim ,-1 -wherein said control -meansl'isfconstructed-and-arranged -so ,as to 1 impart f-tosaid-cathode t ray tube ..a non-linear .characteristic 1 approximating l.a square i law relationship and wherein said output. wave. iderivingmeanscomprises a-signal:.patl1' having a bandpass-.characteristic.adapted to f selectively transmitsignals having a frequency-.substantial- 1y equal to tthe--algebraic--sum-of the frequencies of. said second and third signals-and=a'third-frequencyrepresenting the rate ofscanning said ybeamtover-saidV spaced-portions. v

3. A 'cathode-ray tube f system as A'claimed 1in-.claim 'f 1 1further comprisingv means to apply tosaid control means a' fourth signall having-a frequencyequalL-totheaalgebraic Asum of the frequencies of-,said-second-and1mird=-signals.

l4. -A cathode-raytube system "forlproducing--a-'color y' ltelevision image-comprising -at eathode-rayl tube' -having-.a source of an-'electron' beam, control means tonvaryathe intensi-ty'of: the-beam, a'bea-ml intercepting structure-comj prisingconsecutively arranged portions, each comprising lal plurality ofstripesof-uorescent :material teach of said Vstripesproducinglight-of -a different color.- -uponimp-ingement bysaid beam,-said structure havingsecond-portions thereof spaced apart-and comprising a Amaterialahaving ra-given response characteristic ywhen said-beam impinges `thereon, and-means to-iproduce an output-signalindicative of-y intensitysvariations ofsaid beam and of-fthesaid given response f characteristic, said control means being constructed-and-l arranged -toimp'art to` said cathode ray tube a non-linear beam-current versus control-voltage characteristic producing non-linear interaction of the intensity variations of said beam when a plurality of signals are applied to said control means, means for periodically deilecting said beam across the beam intercepting structure to thereby scan said beam over said first and second portions, means for producing a first signal comprising a Video color wave having a frequency spectrum of a given maximum extent and including a component having a frequency within said spectrum approximating the rate of scanning said rst portions, means for producing a second signal having a frequency greater than and widely diferent from the maximum frequency of said rst signal, means for producing a third signal having a frequency greater than the maximum frequency of said first signal and differing from the frequency of said second signal by a predetermined value, means for applying said first, second and third signals to said control means, and means coupled to said output signal means for deriving therefrom a wave having a component established by said second and third signals and by the rate of scanning of said beam over said spaced portions.

5. A cathode ray tube system for producing a color television image as claimed in claim 4 wherein said control means is constructed and arranged to impart to said cathode ray tube a non-linear characteristic approximating a square law relationship, and wherein said output wave deriving means comprises a signal path having a bandpass characteristic adapted to selectively transmit signals having a frequency substantially equal to the algebraic sum of the frequencies of said second and third signals and a third frequency representing the rate of scanning said beam over the spaced portions.

6. A cathode-ray tube system for producing a color television image as claimed in claim 4, further comprising means to apply to said control means a fourth signal having a frequency equal to the algebraic sum of the frequencies of said second and third signals.

7. A cathode-ray tube system for producing a color television image as claimed in claim 4 wherein said third signal has a frequency value between the maximum frequency value of said rst signal and the frequency value of said second signal, wherein said output wave has a frequency substantially equal to the difference between first and second frequency values, said rst frequency value being equal to the difference between the frequencies of said second and third signals and said second frequency value approximating the rate of scanning said second portions, and further comprising means to apply to said control means a fourth signal having a frequency value equal to said first frequency value.

8. A cathode-ray tube system for producing a color television image, comprising a cathode-ray tube having a source of an electron beam, control means to vary the intensity of the beam, a beam intercepting structure comprising consecutively arranged portions, each comprising a plurality of stripes of fluorescent material, each of said stripes producing light of a different primary color upon impingement by said beam, said structure having second portions thereof spaced apart and comprising a material having a given response characteristic when said beam impinges thereon, and means to produce an output signal indicative of intensity variations of said beam and of the said given response characteristic, said control means having a non-linear beam-current versus controlvoltage characteristic producing non-linear interaction of the intensity variations of said beam when a plurality of signals are applied to said control means, means for periodically deecting said beam across said beam intercepting structure to thereby successively scan said beam over the said first and second portions, means to generate a pilot carrier Wave of a given rst frequency, means to produce a iirst color video wave having a component at the frequency of said pilot carrier wave, means to combine said first color video Wave and said output signal to produce a second color video Wave having a component at a frequency approximating the rate of scanning of said second portions, means to generate an index control wave of a given second frequency greater than said iirst frequency, means to combine said pilot carrier Wave and said index control Wave to produce a heterodyne Wave having a frequency equal to the algebraic sum of the said first and second frequencies, means to apply to said control means said second color video Wave, said index control Wave and said heterodyne wave, and means to derive from said output means said output signal havn ing a frequency equal to the algebraic sum of the frequency of said pilot Wave and a frequency representative of the rate of scanning said beam over said spaced portions.

9. A cathode-ray tube system for producing a color television image as claimed in claim 8 further comprising means to apply said pilot carrier Wave to said control means.

References Cited in the file of this patent UNITED STATES PATENTS 2,415,059 Zworykin Jan. 28, 1947 2,490,812 Huffman Dec. 13, 1949 2,530,275 Weingarten Nov. 14, 1950 2,530,431 Huifman Nov. 21, 1950 2,545,325 Weimer Mar. 13, 1951 2,621,244 Landon Dec. 9, 1952 2,635,140 Dome Apr. 14, 1953 

